The use of exogenous gonadotropic hormones has permitted the artificial induction of sexual activity and ovulation in the laboratory mouse and cat. Embryonic material from the former species is being applied to developmental studies permitting in vitro culture, manipulation, chronic cryopreservation of various inbred strains and the eventual recovery of such material for rederiving valuable models for future investigative research. Mouse embryos, freeze preserved in liquid nitrogen, thawed after 2 years storage and transferred into recipient females, have resulted in healthy, normal offspring. Technological advances in the mouse system are being applied and extended to the laboratory cat, a species previously shown to be an excellent model for the study of leukemia and sarcoma. Feline embryos at the morula stage of development have been collected and successfully cultured to the advanced blastocyst state in vitro. Methods for micromanipulation of the embryo will eventually be developed to allow microinjection of molecularly cloned genes which participate in transformation and inborn errors.